Differential stages are used in many applications of which a few representative ones are given.
For use in analog signal processing, see for example:
(1) Wong & Ott: Function Circuits, McGraw-Hill Book Co., 1976 PA0 (2) Blackmer, D. E.: Multiplier Circuits, U.S. Pat. No. 3,714,462 PA0 (3) Solomon & Davis: Automatic Gain Control Amplifier, U.S. Pat. No. 3,684,974 PA0 (4) Wong & Ott: Function Circuits, McGraw-Hill Book Co., 1976. PA0 (5) Blackmer, D. E.: Multiplier Circuits, U.S. Pat. No. 3,714,462. PA0 (6) In high frequency technology with automatic gain control (AGC) circuits--see the aforementioned Solomon & Davis "Automatic Gain Control Amplifier", U.S. Pat. No. 3,684,974.
In analog computer technology, for example for logarithmic circuits, anti-log circuits, and multipliers--see:
In audio technology, e.g. for voltage controlled amplifiers--see:
In voltage-controlled, voltage-current transfer circuits, in control technology, for integrators with voltage-controlled time constant; in filter technology, for filters with voltage-controlled limiting frequency, and in instrumentation, for function generators and sinusoidal oscillators with controlled frequency--see the above reference.
Ordinary differential circuits frequently do not have exact exponential relationship between control voltage to the base of the transistor circuit and the collector current; this, apparently, is due to the base connection resistances, and emitter contact and connection resistances. These connection resistances are also referred to as bulk resistances. The voltage drops over these resistances can be compensated--see the "Wong & Ott" reference above. This reference discloses that the error due to the voltage drop on the emitter and the base bulk resistances can be compensated by applying an equal and opposite voltage to the base of the transistor which generates the logarithmic function.
Compensating circuits as previously known have the disadvantage that the base connections of the transistors are used for compensation and thus cannot be connected to other circuits according to freely selectable design requirements. Compensation can be carried out with resistors only if a voltage proportional to the current through these resistors is available. The voltage, additionally, must be of the proper polarity. Junctions with a proportional voltage are loaded by the current flowing through the resistors.
The additional transistors are connected in parallel and thus cause twice the current which then must be connected through a current mirror circuit. Compensation at high frequency becomes inaccurate and is difficult to uses in integrated networks. The compensation error is additionally a function of temperature and is different in NPN and PNP differential circuits.